Ophicleide Posted October 5, 2015 Share Posted October 5, 2015 Hi All, Although I'm a newb, I'm thinking of fitting in a digital voltmeter to my TG when it arrives, as well as the shunt mod. I'm just a little nervous about the concept of being thrown off the EUC at low voltage and it would be nice to look down and see a number instead of 1, 2, 3 or 4 lights.Has anyone done this kind of thing? Link to comment Share on other sites More sharing options...
esaj Posted October 5, 2015 Share Posted October 5, 2015 Yup, done it.That's a combined voltage- & current-display (current measuring needs a separate resistor-shunt between the power cable, and that's pretty big), and needs separate power for voltages above 30V DC (hence the battery casing with the red on/off button for the display).The easiest approach is to use a "self-powering" voltage-only display that draws it's usage voltage directly from the measured wires, with large enough voltage range, for example:http://www.aliexpress.com/item/Free-Shipping-0-56-Green-LED-DVM-Voltage-Panel-Meter-LED-4-5-150V-Digital-DC/912492417.htmlThere are different sizes & colors available, I've got one of these also, and another that goes up to 100V... do check that it can power itself up to at least 70V from the measured wires, unless you want to use separate power source, in the above picture I used a 9V battery. Also worth checking that it has calibrating screw behind it (the one I linked has, the other I got doesn't), sometimes the meters can be off when they arrive. Link to comment Share on other sites More sharing options...
Ophicleide Posted October 5, 2015 Author Share Posted October 5, 2015 That's great! I was looking at this one, which has the 0 - 99.9v range I was looking for and is available in 3 LED colours.http://www.banggood.com/Wholesale-Mini-Digital-Voltmeter-Red-LED-Panel-Meter-DC-0V-To-99_9V--p-49602.html Do you find it useful? Link to comment Share on other sites More sharing options...
dmethvin Posted October 5, 2015 Share Posted October 5, 2015 @Ophicleide be careful there, the one you linked needs a separate power input from the monitoring lines. You could probably open up and tap your battery pack but it would be easiest to use the 2-wire style that @esaj linked. Link to comment Share on other sites More sharing options...
Ophicleide Posted October 5, 2015 Author Share Posted October 5, 2015 Thanks, dmethvin! I think the one esaj linked to would be better. Link to comment Share on other sites More sharing options...
Tom Posted October 6, 2015 Share Posted October 6, 2015 Would this realistically help you predict when the battery is unsafe to use? Link to comment Share on other sites More sharing options...
esaj Posted October 6, 2015 Share Posted October 6, 2015 Would this realistically help you predict when the battery is unsafe to use?If you know the voltage where the cut-off occurs, basically yes. But for that you need to know the overdischarge protection voltage, either from the spec-sheet of the BMS or measure it empirically, ie. slowly discharge the batteries with a voltmeter until you see at what voltage the cut-off occurs, taking into account that you need to add some +- to the value, due to variance occurring with different temperatures etc, and the voltmeter or the display in the wheel may not be 100% accurate. Also remember that the voltage sag will be deeper the more empty the batteries are and the more current is being pulled from them. For example with my Firewheel, the voltage doesn't drop but about 1-3V when the "voltage at rest" (voltage when the wheel is stationary) is somewhere above 63V and climbing hills or doing fast accelerations. Then, when the voltage has dropped to between 54-55V (almost empty battery, soon after this the battery warning will trigger and stop me from riding), it will drop more like 5-8V when more current is required. This was with three battery packs (LG MH1-cells, disharge curve: http://www.dampfakkus.de/akkutest.php?id=537 ). So not only do you need to know the voltages, but also "learn" the voltage behavior with your wheel, riding style & batteries to stay completely safe. The dip occurs really fast when you start accelerating or climbing, and sudden spikes in required power can cause even deeper dips (the display won't probably even so them all, as they usually update something like 2-4 times per second). Here the spec sheet for a 16S BMS says that the overdischarge protection voltage is 2.70V +- 0.05V per cell, so varies between 2.65 and 2.75V. According to that, the highest total voltage for the pack where the protection can trigger should be 2.75V * 16 = 44V, and at the "latest", it should trigger at 2.65V * 16 = 42.4V. With a voltage-meter in your wheel, you could then stop riding when you see the voltage starting to dip "too near" the upper value to stay safe. Link to comment Share on other sites More sharing options...
Maxime Posted October 8, 2015 Share Posted October 8, 2015 ESAJ, I am surprised you have a Charge Doctor, but not allready shunted you wheel to avoid your mind-torturing preoccupations and run mind-free, looking at trees, flowers and birds...Unless you are opposed by fear to burn your wheel and your person or just some parts of…Since I shunted, I have had no problem, even if I have put my wheel in water mid-height and had a temporarily failure. But no burn, just let it dry open. Link to comment Share on other sites More sharing options...
esaj Posted October 8, 2015 Share Posted October 8, 2015 ESAJ, I am surprised you have a Charge Doctor, but not allready shunted you wheel to avoid your mind-torturing preoccupations and run mind-free, looking at trees, flowers and birds...Unless you are opposed by fear to burn your wheel and your person or just some parts of…Since I shunted, I have had no problem, even if I have put my wheel in water mid-height and had a temporarily failure. But no burn, just let it dry open.Yes, I bought mine from Hobby16 during the summer, also, the original batteries are shunted. This picture is taken with a custom battery-set (3*192Wh, currently 4*192Wh), which still needs some work, and I don't want to lose the warranty yet (so those aren't shunted yet). The original idea for using the volt-meter is because it's more accurate than the nearly useless 0-99% -battery display of Firewheel. Link to comment Share on other sites More sharing options...
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